1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to an MISFET (Metal Insulator Semiconductor Field Effect Transistor)
2. Description of the Related Art
In recent years, with miniaturization of semiconductor devices, an increase in speed of an MISFET has attracted attention. For example, in a CMOSFET (Complementary MOS Field Effect Transistor), a carrier (hole) mobility in a channel region of a p-channel MOSFET (which will be referred to as a pMOS hereinafter) is slower than a carrier (electron) mobility in a channel region of an n-channel MOSFET (which will be referred to as an nMOS hereinafter), and hence increasing a speed of the pMOS is demanded.
On the other hand, in the pMOS, it is known that using a silicon germanium as a compound of silicon and germanium having a larger atomic radius than silicon for a source/drain layer provides a compression stress to a channel region and improves a carrier mobility, and that forming a silicide film on the source/drain layer of silicon germanium can reduce a resistance of the source/drain layer (see, e.g., P. R. Chidambaram et. al.; “35% Drive Current Improvement from Recessed-SiGe Drain Extension on 37 nm Gate Length PMOS”, 2004 Symposium on VLSI Technology Digest of Technical Papers, pp. 48-49).
In this conventional technology, however, when forming the silicide film on the source/drain layer, since the silicon germanium and the silicide film have poor affinity, an increase in a junction leakage current or a contact failure may possibly occur. That is, when, e.g., a nickel silicide film is formed on the silicon germanium, a ternary compound of NiSiGe is formed between them. However, since this compound is thermally unstable, aggregation of Ni or deterioration in surface morphology occurs, a junction leakage current is increased, and unevenness of a contact resistance becomes considerable on, e.g., an interface of the compound and the nickel silicide film. As a result, a problem of deterioration in transistor characteristics may occur.